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February 2, 2016

The World

Excerpts from the Discussion on PL Quality from The Shrimp List

 

Here are some of the most recent entries from The Shrimp List discussion on postlarvae quality:

 

J. Michael Mogollon (jmmogollon@aol.com): I think a well screened PL batch, where the screening includes microscopic observation, swimming behavior observations, size disparity calculation—and then a stress test, is a good practice.  However all that good work only gets you to “1st base”.  To get to “2nd base”, you have to deal with the myriad of possible effects that the selected PL batch will be faced with in the pond.  That will determine whether or not you ever reach home plate.  Looking for a direct correlation between PL batch “quality” and final pond performance is not straightforward.  The pond environment is never the same even from one day to the next, and even less so from one pond to a neighboring one.  So you have to break down the pond process and manage each part very well...picking good PLs is key, but only a small first step.

 

I do think there is a serious overall problem in PL vigor.  My hunch is that there is a loss of heterozygocity.  Broodstock needs to be clean—that is SPF—but their bloodlines need continuous infusions of genes from parallel programs that are starting with hardy stocks and turning them into SPF.  There are too many diseases out there, and closing ourselves off from the natural selection process occurring in the wild seems foolish and unnecessary.  I think that is where we are today, except for some programs, like those in Ecuador.

 

Madhu Raju (mkraj6@yahoo.com): Since last year, we are facing similar problems in India.  The broodstock comes from USA, and it is very bad.  Even if the ponds are very good, we get poor survivals and very slow growth rates.  Feed conversion ratios are increasing.  The feed companies must be happy.  We don’t know when government will wake up to this issue.

 

Eric Muylder (eric@crevetec.be): In an ideal situation, the hatchery and farm should belong to the same company.  Then, if there are no production bonuses to get in the way, the hatchery will know which batches are good enough to stock in the ponds and which ones that should be discarded.  When I was working in Seychelles, 100 PLs were stocked in a small net in the pond, and if survivals were less than 85 % after 24 hours, the pond was emptied.  The farm managers knew from previous years that it was not worth it to invest in low-quality PLs because they would continue dying at rates of 5-10 % per week even when they reached 15 grams or more.  We were working with Penaeus monodon, and the low-quality batches mostly came at the end of a hatchery cycle, so we would close down the hatchery, dry out and start over.

 

When the hatchery and farm are two different companies, the hatchery might be tempted to sell a low-quality batch of PLs.  Hatcheries that consistently sell low-quality PLs will eventually loose all their customers.  Unfortunately, farms in the USA and EU do not have a choice of hatcheries, and the only supplier ships out whatever it has.

 

Source: The Shrimp List (a mailing list for shrimp farmers).  Subject: Quality of PL11 and Subsequent Growth.  January/February 2016. 

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